/in/foo.cc: In function 'int main()':
/in/foo.cc:24:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(k>sum)
        ~^~~~
/in/foo.cc:31:17: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long long unsigned int' [-Wformat=]
  printf("%d",ans);
                 ^